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28 .\" From: @(#)socket.2 8.1 (Berkeley) 6/4/93
36 .Nd create an endpoint for communication
42 .Fn socket "int domain" "int type" "int protocol"
47 creates an endpoint for communication and returns a descriptor.
51 argument specifies a communications domain within which
52 communication will take place; this selects the protocol family
54 These families are defined in the include file
56 The currently understood formats are:
58 .Bd -literal -offset indent -compact
59 PF_LOCAL Host-internal protocols (alias for PF_UNIX),
60 PF_UNIX Host-internal protocols,
61 PF_INET Internet version 4 protocols,
62 PF_INET6 Internet version 6 protocols,
63 PF_DIVERT Firewall packet diversion/re-injection,
64 PF_ROUTE Internal routing protocol,
65 PF_KEY Internal key-management function,
66 PF_NETGRAPH Netgraph sockets,
67 PF_NETLINK Netlink protocols,
68 PF_BLUETOOTH Bluetooth protocols,
69 PF_INET_SDP OFED socket direct protocol (IPv4),
70 AF_HYPERV HyperV sockets
73 Each protocol family is connected to an address family, which has the
74 same name except that the prefix is
78 Other protocol families may be also defined, beginning with
80 with corresponding address families.
82 The socket has the indicated
84 which specifies the semantics of communication.
88 .Bd -literal -offset indent -compact
89 SOCK_STREAM Stream socket,
90 SOCK_DGRAM Datagram socket,
91 SOCK_RAW Raw-protocol interface,
92 SOCK_SEQPACKET Sequenced packet stream
97 type provides sequenced, reliable,
98 two-way connection based byte streams.
99 An out-of-band data transmission mechanism may be supported.
103 datagrams (connectionless, unreliable messages of
104 a fixed (typically small) maximum length).
107 socket may provide a sequenced, reliable,
108 two-way connection-based data transmission path for datagrams
109 of fixed maximum length; a consumer may be required to read
110 an entire packet with each read system call.
111 This facility may have protocol-specific properties.
113 sockets provide access to internal network protocols and interfaces.
116 type is available only to the super-user and is described in
121 Additionally, the following flags are allowed in the
125 .Bd -literal -offset indent -compact
126 SOCK_CLOEXEC Set close-on-exec on the new descriptor,
127 SOCK_NONBLOCK Set non-blocking mode on the new socket
133 specifies a particular protocol to be used with the socket.
134 Normally only a single protocol exists to support a particular
135 socket type within a given protocol family.
136 However, it is possible
137 that many protocols may exist, in which case a particular protocol
138 must be specified in this manner.
139 The protocol number to use is
141 .Dq "communication domain"
142 in which communication
143 is to take place; see
148 argument may be set to zero (0) to request the default
149 implementation of a socket type for the protocol, if any.
153 are full-duplex byte streams, similar
155 A stream socket must be in a
157 state before any data may be sent or received
159 A connection to another socket is created with a
162 Once connected, data may be transferred using
166 calls or some variant of the
171 (Some protocol families, such as the Internet family,
172 support the notion of an
173 .Dq implied connect ,
174 which permits data to be sent piggybacked onto a connect operation by
178 When a session has been completed a
181 Out-of-band data may also be transmitted as described in
183 and received as described in
186 The communications protocols used to implement a
189 is not lost or duplicated.
190 If a piece of data for which the
191 peer protocol has buffer space cannot be successfully transmitted
192 within a reasonable length of time, then
193 the connection is considered broken and calls
194 will indicate an error with
198 in the global variable
200 The protocols optionally keep sockets
202 by forcing transmissions
203 roughly every minute in the absence of other activity.
204 An error is then indicated if no response can be
205 elicited on an otherwise
206 idle connection for an extended period (e.g.\& 5 minutes).
209 signal is raised if a process sends
210 on a broken stream, but this behavior may be inhibited via
214 sockets employ the same system calls
221 calls will return only the amount of data requested,
222 and any remaining in the arriving packet will be discarded.
227 sockets allow sending of datagrams to correspondents
231 Datagrams are generally received with
233 which returns the next datagram with its return address.
237 system call can be used to specify a process group to receive
240 signal when the out-of-band data arrives.
241 It may also enable non-blocking I/O
242 and asynchronous notification of I/O events
246 The operation of sockets is controlled by socket level
248 These options are defined in the file
254 system calls are used to set and get options, respectively.
256 A -1 is returned if an error occurs, otherwise the return
257 value is a descriptor referencing the socket.
261 system call fails if:
264 Permission to create a socket of the specified type and/or protocol
266 .It Bq Er EAFNOSUPPORT
267 The address family (domain) is not supported or the
268 specified domain is not supported by this protocol family.
270 The per-process descriptor table is full.
272 The system file table is full.
274 Insufficient buffer space is available.
275 The socket cannot be created until sufficient resources are freed.
277 User has insufficient privileges to carry out the requested operation.
278 .It Bq Er EPROTONOSUPPORT
279 The protocol type or the specified protocol is not supported
282 The socket type is not supported by the protocol.
308 .%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
313 .%T "BSD Interprocess Communication Tutorial"
324 standard specifies only the
329 constants for address families, and requires the use of
337 flag is expected to conform to the next revision of the
345 constants, and other address families are
351 system call appeared in